There are many means of stabilizing, moving, and lengthening bone. The need arises to stabilize, move and/or lengthen (collectively “lengthen”) bone in a variety of situations, for example, to increase stature, even the length of a pair of limbs, and when a section of bone is removed following illness or trauma. Intercalary defects in long bones may occur as a result of trauma or after the resection of tumors or infection. With appropriate mechanical fixation, these defects may be managed by autogenous bone grafting, segmental allograft reconstruction, or reconstruction using endoprostheses. Autogenous bone grafting has the disadvantage of donor site morbidity including pain, increased blood loss, and surgical scarring. Furthermore, in the case of large defects it may be difficult or impossible to obtain an optimal volume of autogenous bone. While allografting eliminates the problem of adequate quantity, the incidence of complications such as infection, fracture, and non-union is increased. The risk of exposure to HIV or hepatitis is another concern.
In 1954 Ilizarov reported that mature bone can be elongated by gradual distraction of a fracture callus and called this process distraction osteogenesis. The application of this technique in the form of bone segment transport can obviate the need for open bone grafting in many large diaphyseal defects. However, transfixing wires used in this technique can cause significant complications including wire site infection, pain, and restricted joint motion due to the transfixation of tendons and muscles. These complications are particularly relevant when the Ilizarov device is applied to the femur.
In 1990 Brunner reported that distraction osteogenesis was achievable using intramedullary fixation in sheep tibiae. Brunner's method still relied on the use of an external fixator to provide the force necessary for bone transport. Brunner's work implied that transfixing wires used for internal fixation could potentially be eliminated.
Betz described the use of a telescoping intramedullary rod for distraction osteogenesis. With the Betz device, the patient apparently turned a small knob that protruded from the patient's hip in order to telescopically move the parts relative to one another.
Many bone lengthening devices have actuators or external fixators that penetrate the soft tissue of a patient and extend outside the body. For example, U.S. Pat. No. 5,429,638, which is incorporated herein by reference in its entirety, including any references cited therein, discloses a device for bone transport requiring a cable mechanism. The cable mechanism includes a cable that extends through the soft tissue to just under the skin. The bone is lengthened by a magnet that activates the actuator located under the skin, which in turn causes the implanted device to extend. Such a mechanism can cause infection and discomfort at the site where the cable penetrates the soft tissue.
There are several internal lengthening devices that have been patented, but none of the devices address the problem of transfixing a moving middle segment of bone along the length of a rod without changing the overall length of the rod. U.S. Patent Application No. 20040138663, which is incorporated herein by reference in its entirety, including any references cited therein, discloses a two-part telescopic intramedullary orthopedic device that connects two adjacent fractured or severed bones that can be moved toward or away from each other. The movement is actuated by an external magnetic field, such that one section may be moved axially in relation to the other section. U.S. Patent Application No. 20050261779, which is incorporated by reference in its entirety, including any references cited therein, discloses a rod-like prosthesis that can be expanded non-invasively by an externally applied magnetic field. The rod prosthesis is placed where a segment of bone was removed. The prosthesis is then extended.
Other patents and applications, such as U.S. Pat. Nos. 5,704,939, 6,336,929, and 6,796,984; French Patent No. 2726460; European Patent No. 0869473; and PCT Application No. 0164119, each of which is incorporated herein by reference in its entirety, including any references cited therein, disclose intramedullary devices that connect two bone segments and permit bone elongation between the two bone segments. However, none of them allow a third middle segment of bone to move in a bidirectional mode upon rotation of an external magnet.
Other patents, such as U.S. Pat. Nos. 5,356,411, 5,626,581, and 5,704,938, each of which is incorporated herein by reference in its entirety, including any references cited therein, disclose devices using fluid actuators having fluid containers which are filled by fluid reservoirs in order to cause one section of the device to be moved axially in relation to another section.
The pins, wires, cables, and other structures (herein collectively “pins”) that penetrate the soft tissue in the prior art are sources of infection. This causes problems with joint contractures secondary to the transfixing of these soft tissues. The invention would allow for the middle segment of bone to be transported without the pins transversing the soft tissues, thus eliminating many post operative complications including pin tract infections, pain, and joint contractures. The pins dragging through the skin also causes large scar tracts to be formed which are unsightly and often require surgical excision. The invention eliminates this occurrence and thus the need for scar revision surgery.